LR Powered USB Isolator

Project in progress ETA 1 month or so…

IntroThis is a pretty short and simple project for me – as you might be able to guess from the title it’s essentially an adaption of the USB isolator by Circuits@Home except with the whole switching power supply section cut out and a LM340-5.0 based linear regulator section spliced in there instead. Full credit goes to Circuits@Home for an overall excellent design; I kept most of their board layout intact with only the power section changed. I intend for this thing to be used as a sort of isolator dongle for USB DAC headphone amplifiers; this will enable you to get clean 5V power from a linear regulator rather than from the PC USB bus. The design is kept very low profile with the use of mostly SMD parts and the board is overall slightly smaller than the original one by Circuits@Home.

Parts ListI won’t go into too much detail here as it is a relatively straightforward build and I encourage you to go out and find your own parts from the links to the side rather than just copying and pasting the part numbers I have written down below.

5V fixed SOT-223 form factor VREG. Ground plane of the board serves as a heatsink for this guy. You can get samples of these from National Semi or buy some from any of the big parts vendors Mouser Part #926-LM340MP-5.0/NOPB You could use another SOT-223 fixed 5V VREG in this position if you want but I believe that the LM340-5.0 is a very good part in general.

1N4001 Diode

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Protection diode for VREG – you can find these guys pretty much anywhere. I have a bunch that I got for cheap from thaishopetc Mouser Part #512-1N4001

24Ω 1% tolerance 1206 SMD Resistor

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I’m using Vishay CRCW120624R0FKEA from Mouser

1MΩ 1206 SMD Resistor

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I’m using Vishay CRCW12061M00FKEA parts from Mouser

MLCC 0.1uF X7R 1206 SMD Capacitor

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Bypass capacitors – a fairly common part that you can find around anywhere I’m using Vishay VJ1206Y104KXAMC parts from Mouser

MLCC 0.22uF X7R 1206 SMD Capacitor

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Optional additional bypass for the VREG I’m using Vishay VJ1206Y224KXATW1BC parts from Mouser

MLCC 10uF X7R 1206 SMD Capacitor

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Serves as a power reservoir for the circuit – would’ve been better to just use a bit electrolytic here but I wanted to keep things low profile I’m using Taiyo Yuden TMK316B7106KL-TD parts from Mouser

PWRLED – 1206 SMD LED

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Pretty much any 1206 SMD LED will do; I have a bunch laying around from Sky-Electronic Mart Something like Mouser Part #696-SML-LX1206IC should work

RLED – 1206 SMD Resistor

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Value depends on the specs of the LED you choose (will probably end up something like 150-220Ω) LED Calculator Link: http://ledz.com/?p=zz.led.resistor.calculator (supply voltage is 5V) I’m using a 180Ω Vishay CRCW1206180RFKEA parts bought from Mouser with my LEDs that have a FV of 2.2V and FC of 20mA.

Wall Wart Adapter

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Needs a 2.1mm ID / 5.5mm OD plug which is fairly common It is critical that you use a power supply with center barrel positive, otherwise when you plug it into this board bad things will happen. I’m using the Triad Magnetics WDU75-800 which can be bought from Mouser

Assembly Basic assembly procedures are more or less the same as with Circuits@Home’s original design: http://www.circuitsathome.com/adum4160-usb-isolator-assembly-guide Those new to soldering may need a bit of help from someone more experienced or perhaps some extra practice with soldering down SMD parts. Those experienced with soldering should have no issues with the assembly except for potentially with soldering of the main USB isolator chip – alignment of this guy can be a bit tricky. All of the SMD resistors and capacitors are 1206 which is pretty large within the SMD realm so you should have no problems there; the SOT-223 VREG is fairly large as well so you should have no problems there. I’ll follow up with some basic images of the assembly for this particular board within a month or two.